This paper reports on a new methodology for detecting surface cracks in metallic structures by combining a microwave resonant cavity with infrared imaging. The underlying principle is based on crack induced disruptions of microwave wall currents creating localized concentrations of microwave energy. These regions of concentrated energy may, in turn, produce a localized heating in a thin layer of dielectric material placed adjacent to the surface being inspected. Detection of local hot spots via infrared imaging may then be used to infer the presence of a crack or other discontinuity in the surface. This study utilized a numerical simulation of electromagnetic fields within the resonant cavity and the resulting dielectric heating. The objective of the numerical study was to gain insight into fundamental electromagnetic and thermophysical processes on which this NDT scheme was based. The transient 3D Maxwell's equations were solved numerically using the method of Finite Difference-Time Domain to determine electromagnetic field distributions. The energy equation was then solved in order to determine thermal energy deposition and temperature fields in the dielectric layer. The sample numerical simulations indicate that combining microwave heating with thermographic imaging could lead to a viable non- destructive testing instrument for crack detection.